In Unity, we have some special things for coroutines that are additional to normal C#.
for example, we can use
yield return WaitForSeconds(5.f);
to have a coroutine wait 5 seconds before continuing.
What do yield return false; and yield return true; do?
The only possible yield values the scheduler understands are:
- Classes derived from
YieldInstruction(WaitForSeconds,WaitForEndOfFrame,WaitForFixedUpdate,AssetBundleCreateRequest,AssetBundleRequestand Coroutine- a
WWWobject- "any other value" which isn't one of the above.
If "any other value" is yielded (which includes "null" a string value any other basic type such as int, bool, ... or a reference to an arbitrary object which isn't one of the above mentioned) the scheduler will "schedule" the coroutine for the next frame.
The WaitForEndOfFrame and others of the like, are just blank functions that tag the YieldInstruction in order to decide what to do in the engine.
The default case seems to be WaitForEndOfFrame. So if you yield return something that doesn't have a special meaning, such as a bool, it is the same as WaitForEndOfFrame.
There doesn't seem to be any official documentation on this behavior.
rutter commented about another special case: yield return null
All of the Unity Coroutines including yield return null, run before the frame renders except for WaitForEndOfFrame. You can find rutter's awesome answer over at Unity Answers explaining this further (nice diagrams included).
null and WaitForEndOfFrame are the same, but they are actually slightly different, as detailed at the execution order manual page.
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yield return truedoes something special. Butyield return nullsimply pauses for a frame, so I suspect thatyield return falsehas the exact same effect (alsoyield return 0since 0 false null are all the same under the hood) \$\endgroup\$if (0)orif (null), unlike in C and C++. \$\endgroup\$yield return 0works; apparently because of the reason MLM explained \$\endgroup\$yieldkeyword has been around since at least C# 2.0. All Unity does is call it coroutine and handles the generated iterator and the values returned from it in a way that you can cause non-blocking delays in the execution of your code. \$\endgroup\$WaitForSecondsis not declared. As soon as you declare a method calledWaitForSecondsthat takes a float argument and that returns the element type of the enumeration you are implementing, it would compile again. Hence,yieldis not special to Unity. If anything, theWaitForSecondsmethod is special to Unity, but even then, it does not extend the language C#, but is simply an extra method that was written using standard C#. \$\endgroup\$